Something like LM338 but mosfet?

[Johanx2]

Hi, does anybody know a little circuit that makes the same thing that lm338 circuit does? I need a voltage regulator, and I was thinking, why using this thing that heats and its not every efficient, maybe theres something with mosfet that does not even need heatsink, lm338 usually needs a considerable size heatsink. thanks.

Oh! it already has a name! LM2596, what a beautiful thing!

 

[schmitt trigger]

They are called switched mode power supplies....SMPS in shorthand.

Advanced controller units, employing synchronous rectification coupled with modern Mosfets, low loss capacitors and inductors, can readily achieve efficiencies above 95%

 

[betwixt]

Technically you can use a MOSFET in a linear regulator but the heat generated will still be (Vdrop * I) so there is no advantage over the LM338 anyway.
SMPS is the way to go.

Brian.

 

[Johanx2]

Technically you can use a MOSFET in a linear regulator but the heat generated will still be (Vdrop * I) so there is no advantage over the LM338 anyway.
SMPS is the way to go.

Brian.

Do you remember I will to need something like this in order to dimm and shut down the musical led groups? :-D I prefer with something like this, although I finally found that a boost should be better, so more leds are connected in series, and less need for cables and resistor, I need to step up the voltaje from 25v to about 160volts, or at least 80v will be fine, still less wiring. but I jsut observer the step up circuits found on ebay are so expensive, and regular ones only up he voltage no more that 40v, which is not big gaing. I wonder what to use.

 

[betwixt]

Resistors cost almost nothing. You wire LEDs in groups as long as you include a resistor in each of the groups. For example, if your LEDs have a Vf of 3.2V and you have 24V available and you want 20mA to flow, the resistor is (24-3.2)/0.02 = 1040 Ohms. You can add more than one LED in series though, you just add their Vf together and as long as the total is still below 24V it will work exacty the same. For example you could wire six LEDs in series to get a combined Vf of 6*3.2 = 19.2V and use a resistor of (24-19.2)/.02 = 240 Ohms and still only need two wires to connect them. If you need more than six LEDs, wire them in series chains of six, including the resistor, then wire the chains across each other. The calculation per chain is exactly the same and the chains can have different numbers of LEDs as long as you calculate the resistor for that chain accordingly.

So you don't need a higher voltage to light up more LEDs and you can still do it using two wires. You just need a few extra resistors at the LED end of the cable. It's much cheaper that way and it avoids the complications of high voltages and extra power supplies.

Brian.

 

[Johanx2]

thanks, I think you are right, I am going with 6 led groups in series and LM2596 to control and turn off the leds.

 

[betwixt]

No!

Use the LM2956 to provide the regulated voltage you need but not to control the LEDs. It isn't designed for pulsed operation, it is designed to give a steady voltage all the time.
Bear in mind, based on your other thread, you can use much lower voltage to power the filters and comparators circuit, they draw negligible power, and if you use a MOSFET as the LED switch, you can run the LEDs off unregulated power and avoid the need for a complicated power supply altogether.

Brian.

 

[Johanx2]

No!

Use the LM2956 to provide the regulated voltage you need but not to control the LEDs. It isn't designed for pulsed operation, it is designed to give a steady voltage all the time.
Bear in mind, based on your other thread, you can use much lower voltage to power the filters and comparators circuit, they draw negligible power, and if you use a MOSFET as the LED switch, you can run the LEDs off unregulated power and avoid the need for a complicated power supply altogether.

Brian.

the problems is that, I know that I can directly feed the leds after the mosfet, which will give me more than necessary power, the problem is that I also want to dimm the leds (in case I momentarily don't want leds at maximum brightness )and even turn them completely off by dropping off the voltage at a level where leds cannot be turn on because its not enough. Then what should you recommend me? its very easy to put a switch and abruptly disconnect the whole system that cares about the light pulse. I was thinking putting a solid stay relay instead X Y (in schematic) and with it switch the load that is connected on lm338 or LM2596 output, which will be a voltage source controled by a pot, so I will be able to dim my auditorium leds we talked about in the other post, so whit that pot I can control either, brightness and turn them off by turning of the pot, because the voltage will drop the led exciting voltage. Is not it good my idea? are not solid stay relay enough fast? not even being solid? I think yes, sorely they are enough fast for this application, is not?

I was not talking about the lm338 directly connected to the XY section (after the IRF530), which what maybe you thought, so what about a SSrelay instead? and switching the ground leds at music rhythm?

 

[Audioguru]

You do not dim LEDs by reducing the voltage. Instead the current or high frequency pulse widths should be reduced instead. Simply look at the voltage curve of an LED on its datasheet so see than reducing the voltage a tiny amount reduces the brightness a huge amount. But reducing the temperature a small amount also changes the brightness unless the current is not changed.